This week, Ohio voters soundly rejected Gov. John Kasich’s plan to scale back collective bargaining rights for public employees. The vote was a big victory for labor; in particular, it showed how important the nation’s teachers unions have become beyond the classroom. Teachers groups are mobilizing like never before — because they face threats to their very existence.

Teachers unions joined a coalition of workers to produce the ads that helped defeat Issue 2 in Ohio. “How dare those politicians and lobbyists and special interest insiders attack the people who teach our children for a living?” the ads said.

Labor spent millions on the referendum, which overturned restrictions on collective bargaining. According to Kim Anderson of the National Education Association, the teachers group contributed the lion’s share. “More than $10 million,” she says.

The NEA says it’s the biggest labor union in 48 states, with more than 3 million members nationwide. Those numbers help build a big war chest, and, Anderson says, it also means the NEA could contribute lots of foot soldiers to the Ohio fight.

“Folks from at least 20 state affiliates that went into Ohio on their own volition because they wanted to help,” she says.

They’re coming because these collective bargaining fights are a threat to some unions’ ability to exist.

The issue has become more urgent since Wisconsin public workers lost a fight over collective bargaining rights earlier this year. As a result, some locals lost the ability to collect dues automatically from paychecks. Now, hundreds of the state’s teacher locals must hold elections to say whether they want the union to represent them.

That’s why Tuesday’s results in Ohio were important. So was a small but important victory in Michigan. There, the Michigan Education Association mounted a successful recall campaign against a state representative who symbolized the Republican effort to cut spending and limit union power.

“They spent more time vilifying unions and attacking the middle class of this state than they have putting people back to work,” MEA spokesman Doug Pratt says.

“That’s not what they were sent to Lansing to do, and voters are going to hold them accountable for that.”

Former state Rep. Paul Scott, the victim of the recall, says he expected a response from labor. But he was surprised when the union focused its organizing efforts on a recall.

“The most entrenched and well-financed government employee union in any state is going to be the teachers union,” Scott says. “They just immediately went toward my community and started protests.”

The union targeted other lawmakers for recall, but those efforts failed. Displays of union power just give new ammunition to the growing number of anti-union groups and websites, like TeachersUnionExposed.com. Justin Wilson says the website tries to uncover how labor protects ineffective teachers from being fired.

The mission, he says, is “to actually get a hold of proceedings where teachers have been disciplined; to sort of get to the bottom of how many teachers in this country are terminated, working through their onerous collective bargaining agreements that make it nearly impossible.”

This summer the National Education Association increased dues by $10. Some of that money will be directed at preserving bargaining rights. In Wisconsin, teachers are also pushing for their own recall effort against Gov. Scott Walker. These are all expensive battles, but for teachers unions, they are a matter of life and death.